Hardening Operation

: The Working Of Steel

Hardening a gear is accomplished as follows:

The gear is taken from the furnace by the furnaceman and placed in

the lower die, surrounding the centering jaws, as shown at H in

Fig. 62 and C in Fig. 63. Air is then turned into the cylinder

D, and the piston rod E, the die carrier B, the top die F

and the expander G descend. The pilot H enters a hole in the

center of the lower die, and the expander G enters the centering
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jaws I, causing them to expand and center the gear C in the

lower die. On further advance of the piston rod E, the expander

G is forced upward against the pressure of the springs J and

the upper die F comes in contact with the upper surface of the

gear. Further downward movement of the dies, which now clamp the

work securely, overcomes the resistance of the pressure weight

K (which normally keeps up the plunger A), and the gear is

submerged in the oil. The quenching oil is circulated through a

cooling system outside the building and enters the tempering machine

through the inlet pipe L. When the machine is in the position

shown, the oil passes out through the ports M in the lower plunger

to the outer reservoir N, passing to the cooling system by way of

the overflow O. When the lower plunger A is forced downward,

the ports M are automatically closed and the cool quenching oil

from the inlet pipe L, having no other means of escape, passes

through the holes in the lower die and the grooves in the upper,

circulating in contact with the surfaces of the gear and passes to

the overflow. When the air pressure is released, the counterweights

return the parts to the positions shown in Fig. 63, and the operator

removes the gear.

The gear comes out uniformly hard all over and of the same degree of

hardness as when tempered in an open tank. The output of the machine

depends on the amount of metal to be cooled, but will average from

8 to 16 per hour. Each machine is served by one man, two furnaces

being required to heat the work. A slight excess of oil is used

in the firing of the furnaces to give a reducing atmosphere and

to avoid scale.